"Congratulations @JulieAnneGenter ! So pleased to hear of the safe arrival of the newest addition to the parliamentry play group. Hope you enjoy those very special first few days," Ms Ardern said on Twitter.

"Peter and I are delighted to welcome the new addition to our family," Ms Genter said in a statement.

"I want to thank the support I have had from my midwives, and our public health system."

Ms Genter is also Associate Minister of Health and Associate Minister of Transport.

She will take three months of leave from her Ministerial duties, returning on November 16.

Green MP Eugenie Sage has taken over as Acting Minister for Women, and Green Party co-leader James Shaw has taken over as Associate Minister of Health and Associate Minister of Transport.